This invention relates to creation of electrical coronas, and in particular to an electrode arrangement for creation of a corona for surface treating desired areas of plastics and other materials.
As explained in U.S. Pat. No. 4,693,869, the disclosure of which is incorporated herein by reference, many plastics, when molded, will not accept an adhesive, a coating, or inks or other printing vehicles unless the surface of the plastic has been chemically and/or physically altered. The referenced patent discloses an electrode arrangement for creating a corona for treating such surfaces to accept adhesives, coatings, inks or other materials applied to the surface. One form of that patent pertains to a disc-like electrode which is able to create a corona in an annular fashion only because a corona will not be emitted at any location other than the outer periphery of the electrode, thus leaving a circular central area without a treating corona.
U.S. patent application Ser. No. 318,535, filed Mar. 3, 1989, now U.S. Pat. No. 4,924,092, issued May 8, 1990 the disclosure of which is also incorporated herein by reference, is directed to a unique a system for creating a uniform corona over a predetermined volume of free space, so that a plastic or other material can be treated on all sides at one time, rather on only a single side. In both the referenced patent and the referenced application, a high frequency electrical corona generator is used to generate resonant frequencies on the order of 2MHz and above.